page_title: Crop diversity
section_title: Within-crop diversity
hierarchical_section_title: Crop diversity / Within-crop diversity
caption_attribution_description: English: Trinidadian mixed crop cultivation of cacao and banana
context_page_description: Crop diversity is the variance in genetic and phenotypic characteristics of plants used in agriculture. Over the past 50 years, there has been a major decline in two components of crop diversity; genetic diversity within each crop and the number of species commonly grown.
  Crop diversity loss threatens global food security, as the world's human population depends on a diminishing number of varieties of a diminishing number of crop species. Crops are increasingly grown in monoculture, meaning that if, as in the historic Great Famine of Ireland, a single disease overcomes a variety's resistance, it may destroy an entire harvest, or as in the case of the 'Gros Michel' banana, may cause the commercial extinction of an entire variety. With the help of seed banks, international organizations are working to preserve crop diversity.
context_section_description: Within-crop diversity, a specific crop can result from various growing conditions, for example a crop growing in nutrient-poor soil is likely to have stunted growth than a crop growing in more fertile soil. The availability of water, soil pH level, and temperature similarly influence crop growth.
  In addition, diversity of a harvested plant can be the result of genetic differences: a crop may have genes conferring early maturity or disease resistance Such traits collectively determine a crop's overall characteristics and their future potential. Diversity within a crop includes genetically-influenced attributes such as seed size, branching pattern, height, flower color, fruiting time, and flavor. Crops can also vary in less obvious characteristics such as their response to heat, cold, a drought, or their ability to resist specific diseases and pests.
  Modern plant breeders develop new crop varieties to meet specific conditions. A new variety might, for example, be higher yielding, more disease resistant or have a longer shelf life than the varieties from which it was bred. The practical use of crop diversity goes back to early agricultural methods of crop rotation and fallow fields, where planting and harvesting one type of crop on a plot of land one year, and planting a different crop on that same plot the next year. This takes advantage of differences in a plant's nutrient needs, but more importantly reduces the buildup of pathogens.
  Both farmers and scientists must continually draw on the irreplaceable resource of genetic diversity to ensure productive harvests. While genetic variability provides farmers with plants that have a higher resilience to pests and diseases and allows scientists access to a more diverse genome than can be found in highly selected crops. The breeding of monocultural crops steadily reduces genetic diversity as desirable traits are selected, and undesirable traits are removed. Farmers can increase within-crop diversity to some extent by planting mixtures of crop varieties; they can further increase in-field diversity by polycultural practices such as intercropping and companion planting.
caption: Traditional mixed crop (polyculture) cultivation of cacao and banana, Trinidad, 1903
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